1. Field of the Invention
The present invention relates to a transmission board having a transmission circuit on a surface thereof and connection pads on the surface edge for connection with a mating connector and a connector assembly consisting of a connector connected to the transmission board.
2. Description of the Related Art
Generally, a transmission board includes a resinous circuit board with transmission circuit or circuits printed on one or both sides thereof and connection pads provided on an edge of the circuit board for connection with a mating connector. Such a transmission board is disclosed in U.S. Pat. No. 6,171,115; FIGS. 1–2. The edge of the circuit board is tapered so as to facilitate connection between the connection pads and the spring contacts of terminals for a mating connector. The tapered edge is made by planomilling.
The above circuit board, however, has the following disadvantages.
First of all, the processing precision of the tapered edge is very low and the processing requires much labor. The circuit board is so thin that it tends to warp and vibrate upon milling, providing a waving tapered edge or asymmetrical tapered edges on both surfaces. That is, the processing precision is so low that a plurality of terminals have different plugging forces and contact pressures. In addition, the precision in the size of the board itself or the positions of connection pads is so low as to produce a difference between the terminals and the connection pads, preventing miniaturization of a multiple pole connector that has multiple connection pads at high density.
In general, the circuit board is reinforced by mixing glass fibers. When the edge of a circuit board is planomilled, glass fibers project at the tapered portion or powder of the glass fiber or resin adheres to the terminal, making poor contact. The rough surface of the tapered portion prevents smooth movement of the terminals, increasing the plugging force of a multiple terminal connector.
Where transmission circuits are provided on both surfaces of a circuit board, the dielectric loss, which is produced by the resin between the transmission circuit, is so high that the electrical characteristics become poor. Especially, this affects the high-speed transmission. It is noted that the relative permittivity of the resin to air is approximately 4.